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Market Street Retrofit

Spokane , Washington



Spokane County


Spokane County


DW Excavating 



Technical Description:

(15) Filterra® Bioretention Systems

The Market Street - Francis to Lincoln Stormwater Retrofit project involved removing and replacing existing stormwater structures on Market Street between Francis Avenue and Lincoln Road in Spokane County, Washington. The pre-existing drainage system consisted of catch basins and dry wells. The project replaced the catch basins with Filterra Biofiltration systems and bioretention swales that capture and remove stormwater pollutants such as trash and debris, oils and grease, sediments, nutrients, and metals.

In 1974, Congress passed the Safe Drinking Water Act (SDWA), which required the Environmental Protection Agency (EPA) to create the Underground Injection Control (UIC) Program to regulate underground disposal. The purpose of the program is to protect groundwater from contamination by regulating fluids placed in injection wells. The majority of Class V underground injection control (UIC) wells in Washington State are used for stormwater management. The dry wells along this transportation corridor do not meet the current UIC regulations as outlined in the Stormwater Management Manual for Eastern Washington (SWMMEW) as UIC’s have the potential to place contaminants below the root zone so they may reach underground sources of drinking water. In older developments with existing dry wells, stormwater from pollutant-generating sources generally receives no treatment prior to being discharged into the ground to recharge aquifers.

To address this issue, the County replaced 15 catch basins with Filterra Bioretention systems planted with dwarf lilacs. Two of the Filterra systems were Internal Bypass – Curb configurations. The Filterra Internal Bypass – Curb incorporates a curb inlet treatment chamber and an internal high flow bypass in a single structure. Incorporating a high-flow bypass eliminates the need for a separate bypass structure and enables placement on grade or in a “sag” or “sump” condition. The remaining systems were Filterra Standard Offline configurations, the most economical and simplest Filterra configuration. It utilizes a downstream catch basin or curb inlet for bypass flows allowing for the shallowest profile and most flexible design of any Filterra configuration. It is ideal for both new and retrofit projects.

The County selected Filterra based on Washington Ecology General Use Level Designation (GULD) approval, comprehensive technical and field support, plus ease of inspection and maintenance. Contech representatives were on-site for activation and provided maintenance training for the County and the City of Spokane.

Technical Description:

(15) Filterra® Bioretention Systems


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